Polyphenylene sulfide resins, one of highly heat-resistant crystalline resins, have been utilized in the form of a blend with fillers, such as glass fiber, as resin molding materials excellent in heat resistance, chemical resistance, stiffness and inflammability for electrical/electronic/OA components or automotive electronic components.
Particularly in optical pick-up bases contained in compact disc drives or optical housings of copiers as one of mechanical components for optical instruments, which have been produced by metal die casting using aluminum, zinc or the like, there has been a trend in recent years toward conversion of metals to resins from the viewpoint of decrease in weight and increase in productivity of optical instruments. And polyphenylene sulfide resin compositions have come into use most frequently.
However, it is well known that, though polyphenylene sulfide resins have excellent heat resistance and workability, they may give rise to many problems when molded, such as corroding the metal of molds because of the resins being fused in oxygen atmosphere at high temperature during molding, causing stain-like burns on the surface of molds or molded articles or tar-like matter to adhere to the same with the progress of gasification, and in molds having welded joints, causing whitened appearance on the periphery of the welded joints of black colored molded articles when venting deteriorates. The same is true for the polymer alloys that are composed of polyphenylene sulfide and polyphenylene ether.
And besides, in the polymer alloys composed of polyphenylene sulfide and polyphenylene ether, allowing the polyphenylene sulfide to contain polyphenylene ether makes it possible for them to have the advantage of inhibiting flash from occurring during molding, but on the other hand, it also causes a phenomenon, a disadvantage, particularly in the polymer alloys containing inorganic filler that their inflammability extremely deteriorates.
For the polyphenylene sulfide resin compositions having the above described problems, especially the problems of corroding the metal of molds during molding, causing stain-like burns on the surface of molds or molded articles or tar-like matter to adhere to the same with the progress of gasification, and in molds having welded joints, causing whitened appearance on the periphery of the welded joints of black colored molded articles, there have been proposed a number of improvements and ideas in terms of the materials.
As techniques for the above described improvements and ideas, there have been proposed compositions prepared by blending a polyphenylene sulfide resin with an inorganic gas-scavenger (refer to, for example, Patent Documents 1 to 3). Further, to produce effects of preventing tar-like matter to adhere to molds during molding and of improving the appearance resulted from the gasification, there have been proposed resin compositions composed of polyphenylene sulfide and a specific compound or inorganic filler (refer to, for example, Patent Documents 4 to 6).
These documents disclose attempts to overcome the disadvantages of polyphenylene sulfide resins as base materials by blending the resins with additives. In other words, they disclose attempts to improve the appearance of molded articles by preventing the metal surface of molds from corroding, stain-like burns from being produced on the surface of molds or molded articles and tar-like matter from adhering to the same. However, these methods are no more than means of masking the causative substances, and when molding is performed for a long time under molding conditions where venting is poor, molded articles have extremely deteriorated appearance because stain-like burnings are still produced particularly on the welded joints or their periphery and whitening phenomenon occurs on the black-colored parts. Thus, the actual situation is that molded articles produced by such methods still have a number of problems unsolved.
It is also known, as another problem, that molding polyphenylene sulfide resins involves production of significant flash on the resultant molded articles. This is one of the factors that decrease the productivity/economy in the industrial production of parts.
Polyphenylene sulfide resins are classified into two types, linear (straight chain) and crosslinked (including semi-crosslinked), depending on production process. The latter ones, crosslinked polyphenylene sulfide resins, are thermoplastic resins prepared by producing the former ones, linear polyphenylene sulfide resins, by polymerization and heat treating the linear polyphenylene sulfide resins at temperatures equal to or lower than the melting point of polyphenylene sulfide resins in the presence of oxygen to accelerate the oxidation crosslinking so that the molecular weight and viscosity of the polymer are appropriately increased. They are superior to linear polyphenylene sulfide resins in mechanical strength and heat resistance, but have the disadvantage of being inferior in toughness. On the other hand, in linear polyphenylene sulfide resins superior in toughness, their molecular chain length is hard to increase, due to technological restriction in polymerization, and therefore improvements in mechanical strength and heat resistance cannot be desired. Besides, they have the problem of being more likely to cause flash during the molding.
It is well known that flash on molding is more likely to occur in polyphenylene sulfide resins than in amorphous thermoplastic resins, though there is a little difference between linear ones and crosslinked ones.
Optical pick-up bases contained in compact disc drives or optical housings of copiers as one of mechanical components for optical instruments have been produced by metal die casting using aluminum, zinc or the like; however, in recent years, progress toward the conversion of metals to resins is being made from the viewpoint of decrease in weight and increase in productivity of optical instruments. And in terms of the conversion of metals to resins, materials are needed which provide resin molded articles with high heat resistance and high dimensional accuracy with respect to temperature change and are less likely to cause flash during molding.
Thus, for polyphenylene sulfide resin compositions, as raw materials for the molded articles for the above described applications, there have been proposed a number of improvements and ideas in terms of their materials. To inhibit the occurrence of flash, a big problem caused during molding, a number of techniques have been proposed in which polymer alloys are formed using a polyphenylene sulfide resin as a crystalline resin and a polyphenylene ether resin as an amorphous resin.
As such techniques, proposed are, for example, resin compositions which are composed of: a resin component of polyphenylene sulfide and polyphenylene ether; a specific inorganic compound; a fibrous filler; and other inorganic filler and which are less likely to cause flash during molding and have high stiffness and high dimensional accuracy (referrer to, for example, Patent Documents 7 to 8). To obtain the similar effects, resin compositions are also proposed which are composed of: a resin component of polyphenylene sulfide and polyphenylene ether; a silane coupling agent; a fibrous filler; and other inorganic filler (refer to, for example, Patent Documents 9 to 10). Further, to obtain a resin composition that allows the deviation of optical axis to be kept small when molded into optical components (refer to Patent Document 11), a resin composition is proposed in which the volume fractions of the polyphenylene sulfide and polyphenylene ether used are specified and inorganic filler is used. Further, to decrease the occurrence of flash at the time of injection molding, a resin composition is proposed in which the proportions of polyphenylene sulfide, polyphenylene ether and glass fiber are specified (refer to Patent Document 12). To obtain a resin composition which is composed of polyphenylene sulfide and polyphenylene ether, is low in water absorption properties and anisotropy, and has excellent dimensional stability, it is proposed that a specific linear polyphenylene sulfide is used in combination with a specific crosslinked polyphenylene sulfide (refer to Patent Document 13). Still further, a resin composition suitable for blow molding is proposed in which not only a linear polyphenylene sulfide and a crosslinked polyphenylene sulfide, but a small amount of other resins is used in combination (refer to Patent Document 14).
The present inventors have already proposed resin compositions, as polymer alloy materials composed of a polyphenylene sulfide resin and a polyphenylene ether resin in which a specific compatibilizer is used (refer to, for example, Patent Documents 15 to 16).    [Patent Document 1] JP-A-59-209644    [Patent Document 2] JP-A-60-1241    [Patent Document 3] JP-A-6-322271    [Patent Document 4] JP-A-2000-265060    [Patent Document 5] JP-A-2001-98151    [Patent Document 6] JP-A-2002-129014    [Patent Document 7] JP-A-9-157525    [Patent Document 8] JP-A-11-106655    [Patent Document 9] JP-A-11-158374    [Patent Document 10] JP-A-2002-69298    [Patent Document 11] JP-A-2001-294751    [Patent Document 12] JP-A-2002-179915    [Patent Document 13] JP-A-2002-121383    [Patent Document 14] JP-A-11-228829    [Patent Document 15] JP-A-1-213359    [Patent Document 16] JP-A-2001-302916    [Patent Document 17] JP-A-09-161737    [Patent Document 18] JP-A-10-053706    [Patent Document 19] JP-A-2002-012764
These documents disclose that the disadvantages of resins are overcome, in other words, deterioration of dimensional accuracy with temperature changes is improved and occurrence of flash during molding is inhibited by allowing the resins to take the form of a composition prepared by blending the resin component of polyphenylene sulfide and polyphenylene ether with a variety of inorganic fillers. However, the actual situation is that improvement in heat resistance, and toughness (impact strength) and mechanical strength are still insufficient.
There are also proposed resin compositions whose toughness has been further improved by adding a copolymer of a vinyl aromatic compound and a conjugated diene compound and/or the copolymer having undergone hydrogenation, as an elastomer component, to a resin component (refer to, for example, Patent Documents 17, 18 and 19).
However, for the proposed resin compositions composed of polyphenylene sulfide, polyphenylene ether, and an elastomer component, though their mechanical properties have been improved, none of their impact resistance, stiffness and heat resistance reaches the higher level required to meet the needs for decreasing the thickness of molded articles to keep up with the recent trend toward smaller-sized, lighter-weight and more precise mechanical parts such as frame chassis in the fields of office equipment or information instruments.